In modern communication systems, clock and data recovery (CDR) is widely applied in optical fiber communication transceivers. The phase locked loop (PLL) is mainly used in the clock and data recovery circuit, and the voltage control oscillator (VCO) is a core component of the phase locked loop and plays a decisive role for the performance of the phase locked loop. The design of the voltage control oscillator of high performance is always a research hotspot. At present, common integrated voltage control oscillators (VCOs) are mainly the inductance-capacitance voltage control oscillator (LC-VCO) and the ring voltage control oscillator (Ring-VCO). The ring voltage control oscillator can be manufactured by using the standard CMOS process, and it is easy to obtain a wide tuning range and multiphase clock output. In some applications (such as multi-clock circuits, on-chip systems and the like), the ring voltage control oscillator has unparalleled advantages.
The ring voltage control oscillator (Ring-VCO) in the conventional phase locked loop circuit is mostly a four-stage amplification circuit, and the number of phases corresponds to the number of stages of the amplification circuit. For example, a clock requiring eight phases uses an eight-stage amplification circuit. A general amplification circuit serves as a delay unit. When the eight-stage delay unit is used to obtain a clock of eight phases, the current consumed is proportional to the number of stages; the larger the power consumption is, the larger the occupied area is; moreover, for the same delay unit, the higher the number of stages is, the lower the speed is, which cannot achieve multi-phase clocks of high speed. Because lengths of connection wires between the stages have larger differences, the parasitic resistances and the capacitances of the connection wires are inconsistent, resulting in different parasitic delays, which ultimately affect different phase differences when a plurality of phase clocks are outputted, resulting in the error rate of data recovery in the application.